The present invention concerns a method for operating a fuel injection system as defined in the preamble of claim 1 and a fuel injection system as defined in the preamble of claim 12.
Fuel injection systems may use piezoelectric actuators or elements, in which the piezoelectric actuators or elements exhibit a proportional relationship between an applied voltage and a linear expansion. Thus, it is believed that using piezoelectric elements as actuators may be advantageous, for example, in fuel injection nozzles for internal combustion engines. The European Patent Specifications EP 0 371 469 B1 and EP 0 379 182 B1 concern the use of piezoelectric elements in fuel injection nozzles.
When piezoelectric elements are used as actuators in fuel injection nozzles (which may be xe2x80x9ccommon railxe2x80x9d injectors) of an internal combustion engine, fuel injection may be controlled by applying voltages to the piezoelectric actuators or elements, which expand or contract as a function of the applied voltage. As a result, an injector needle that may be connected to the piezoelectric actuators or elements by a transfer arrangement or system is moved up and down so as to open and close an injection nozzle. The application of the voltage may be controlled by a feedback system, which may involve comparing an obtained voltage to a target voltage and ending a corresponding charging procedure when the obtained voltage equals the target voltage.
Control systems for controlling the piezoelectric actuator may include a control arrangement or unit (which may include a central processing unit (CPU)), at least one controlled piezoelectric element and a utilization arrangement, which transforms the control signals as necessary and applies them to the controlled piezoelectric element. For this purpose, the control arrangement and the utilization arrangement may be connected to each other by a communication arrangement, such as a bus system. Moreover, external data may need to be communicated to the control arrangement and/or the utilization arrangement in a corresponding way.
In the example of a fuel injection nozzle, the expansion and contraction of piezoelectric elements may be used to control valves that manipulate the linear strokes of injection needles. The use of piezoelectric elements, for example, with double-acting, double-seat valves to control corresponding injection needles in a fuel injection system is shown in German Patent Applications DE 197 42 073 A1 and DE 197 29 844 A1, which are incorporated herein in their entirety.
In a fuel injection system, one goal may be to achieve a desired fuel injection volume with sufficient accuracy, especially for small injection volumes, such as, for example, during pilot injection. Using, for example, a double-acting, double-seat control valve, the piezoelectric element may be expanded or contracted by applying an activation voltage so that a corresponding controlled valve plug is positioned midway between the two seats of the double-seat valve to position the corresponding injection needle for maximum fuel flow during a set time period. It is, however, difficult to determine and apply a sufficiently precise activation voltage so that, for example, a corresponding valve plug is accurately or precisely positioned for maximum fuel flow.
Thus, for example, because the xe2x80x9ctravelxe2x80x9d of a piezoelectric element depends on its temperature, the maximum travel may be reduced considerably at very low temperatures (such as, for example, temperatures less than 0xc2x0 C.). Conversely, at high temperatures, the maximum travel may increase. Therefore, in designing a fuel injection system, the temperature dependence should be considered so that any associated deviation may be minimized or at least reduced. If, however, the piezoelectric element temperature is not directly measured, the temperature must be derived indirectly. Since the piezoelectric element capacitance also exhibits temperature response, the capacitance may be used to estimate the piezoelectric element temperature and therefore the desired maximum travel of the piezoelectric actuator or element.
As discussed, piezoelectric actuators or elements may be driven using voltage control. One object of driving piezoelectric actuators or elements is to charge or discharge the actuator within a specified time. In this regard, voltage gradients arise when charging and discharging the piezoelectric actuators or elements, and depend on or are a function of the average charging or discharging currents. Depending on the application, the current gradient may be, for example, on the order of about 10 A/xcexcsec. Since the switches that may be used for the current regulation and driver logic may, for example, have switching times of about 1 xcexcsec, for example, the desired current may be exceeded, for example, by up to about 10 Amps. Therefore, the actual voltage gradient may systematically differ from the desired voltage gradient during the charging and discharging operations so that there is a deviation in the start and the duration of the drive for the fuel injectors.
It is therefore believed that there is a need to correct, eliminate or at least reduce these systematic errors to increase the drive accuracy of the fuel injection components.
It is also believed that there is a need to provide a relatively cost effective or inexpensive and simple method and system to compensate for the systematic errors to increase the accuracy of the fuel injection system, especially during the startup and/or pilot injections.
It is also believed that there is a need to provide a method and system to correct any errors caused by the current cycling hardware during the discharging and charging of the piezoelectric actuators or elements to increase the drive accuracy of the fuel injection components.
It is also believed that there is a need to provide a method and system to xe2x80x9cfreezexe2x80x9d or hold the last output of a drive controller, whether a voltage controller or a voltage gradient controller, during certain conditions so that the drive controller does not xe2x80x9crun upxe2x80x9d against a system xe2x80x9cstopxe2x80x9d and provide incorrect values when the drive controller is enabled again.
Additionally, as discussed above, temperature may affect piezoelectric elements. Piezoelectric elements are, however, capacitive elements that, as discussed above, contract and expand according to a particular charge state or an applied voltage. The capacitance depends, however, on frequency. In this regard, the frequency corresponds to a charge rate (that is, a charge amount per a unit of time) that is delivered to the piezoelectric element. Therefore, in the context of the present application, a time between the beginning and the end of a charging procedure corresponds to the frequency. The capacitance of the piezoelectric should be adjusted to compensate, eliminate or at least reduce its frequency dependence to determine relatively accurate or precise piezoelectric travel based on its capacitance. Otherwise, the determined piezoelectric actuator temperature, and associated maximum travel may be incorrect, which may result in a less precise amount of fuel being injected.
It is therefore believed that there is a need to provide a method and system that compensates for deviations that are caused by any frequency dependence of the capacitance of the piezoelectric elements so that the maximum actuator travel may be estimated with sufficient accuracy so that the drive voltage may be accurately or precisely adjusted.
To facilitate the above, it is believed that there is a need for an apparatus and method for measuring the charge quantity of piezoelectric elements in a timely and accurate way using a measurement and calibration features, which may facilitate diagnosing the piezoelectric actuator or element, and compensating for the temperature and aging characteristics and regulating the reference voltage.
It is also believed that there is a need for an apparatus and method for a timed measurement of the charge quantity across a piezoelectric element, in which the charge quantity across the piezoelectric element is determined or sensed and is provided at a predefined time in synchronization with an injection operation of the piezoelectric element.
An object of an exemplary embodiment of the present invention is directed to providing a fuel injection system with a piezoelectric element for controlling the amount of injected fuel by charging and/or discharging the piezoelectric element, characterized in that the fuel injection system comprises a current flow controller for charging and/or discharging the piezoelectric element based upon the gradient of a voltage across the piezoelectric element due to a charge the piezoelectric element is carrying.
Another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the current flow controller has a desired charging current for charging and/or discharging the piezoelectric element as an output.
Still another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the current flow controller comprises an integrator.
Yet another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the current flow controller comprises a proportional-integrating (xe2x80x9cPIxe2x80x9d) controller.
Still another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the current flow controller comprises at least one charge subcontroller for charging the piezoelectric element based upon the gradient of the voltage across the piezoelectric element and at least one discharge subcontroller for discharging the piezoelectric element based upon the gradient of the voltage across the piezoelectric element.
Yet another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, further comprising a double acting valve being driven by the piezoelectric element, the double acting valve having a first closed position, a second closed position, and an open position, characterized in that the current flow controller comprises a first charge subcontroller for charging the piezoelectric element based upon the gradient of the voltage across the piezoelectric element for moving the double acting valve from the first closed position to the open position and a second charge subcontroller for charging the piezoelectric element based upon the gradient of the voltage across the piezoelectric element for moving the double acting valve from the open position to the second closed position.
Still another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the current flow controller further comprises a first discharge subcontroller for discharging the piezoelectric element based upon the gradient of the voltage across the piezoelectric element for moving the double acting valve from the second closed position to the open position and a second discharge subcontroller for discharging the piezoelectric element based upon the gradient of the voltage across the piezoelectric element for moving the double acting valve from the open position to the first closed position.
Yet another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the current flow controller comprises a hold element capable of keeping the output of the current flow controller at a constant value.
Still another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the charge subcontroller and/or the discharge subcontroller comprises a hold element capable of keeping its output at a constant value.
Yet another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, with a piezoelectric element for controlling the amount of injected fuel by charging and/or discharging the piezoelectric element to a voltage, characterized in that the fuel injection system comprises a voltage controller for controlling the voltage based upon a desired and a measured value of the voltage.
Still another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the voltage controller controls the voltage based upon a desired value of the voltage and a measured value of the voltage associated with a former injection.
Yet another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the voltage controller controls the voltage based upon a desired value of the voltage and a measured value of the voltage associated with a previous injection of fuel.
Still another object of an exemplary embodiment of a method of the present invention is directed to providing a method for operating a fuel injection system with a piezoelectric element for controlling the amount of injected fuel, in particular for operating a fuel injection system according to one of the above fuel injection systems, wherein the amount of injected fuel is controlled by charging and/or discharging the piezoelectric element, characterized in that the piezoelectric element is charged and/or discharged based upon the gradient of a voltage across the piezoelectric element due to a charge it is carrying.
Yet another object of an exemplary embodiment of a method of the present invention is directed to providing a method for operating a fuel injection system with a piezoelectric element for controlling the amount of injected fuel, in particular for operating a fuel injection system according to one of the above fuel injection systems, wherein the amount of injected fuel is controlled by charging and/or discharging the piezoelectric element to a voltage, characterized in that the voltage is controlled based upon a desired and a measured value of the voltage.
An object of an exemplary embodiment of the present invention is directed to providing a fuel injection system with a piezoelectric element for controlling the amount of injected fuel by applying a voltage to the piezoelectric element, characterized in that the fuel injection system comprises a control unit for adjusting the applied voltage based upon a nonlinear relationship between the applied voltage and the charging time.
Another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the nonlinear relationship between the applied voltage and the charging time is based upon a dependency of a capacitance of the piezoelectric element on the charging time.
Still another object of an exemplary embodiment of the present invention is directed to providing a fuel injection system with a piezoelectric element for controlling the amount of injected fuel by applying a voltage to the piezoelectric element, characterized in that the fuel injection system comprises a control unit for adjusting the applied voltage based upon a dependency of a capacitance of the piezoelectric element on the charging time.
Yet another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the fuel injection system comprising a current measuring unit for measuring a current for charging the piezoelectric element.
Still another object of an exemplary embodiment of the present invention is directed to providing the above fuel injection system, characterized in that the control unit further adjusts the applied voltage based upon a current for charging the piezoelectric element.
Yet another object of an exemplary embodiment of a method of the present invention is directed to providing a method for operating a fuel injection system with a piezoelectric element for controlling an amount of injected fuel by applying a voltage to the piezoelectric element, characterized in that the applied voltage is adjusted based upon a nonlinear relationship between the applied voltage and the charging time.
Still another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that the nonlinear relationship between the applied voltage and the charging time is based upon a dependency of a capacitance of the piezoelectric element on the charging time.
Yet another object of an exemplary embodiment of a method of the present invention is directed to providing a method for operating a fuel injection system with a piezoelectric element for controlling an amount of injected fuel by applying a voltage to the piezoelectric element characterized in that the applied voltage is adjusted based upon a dependency of a capacitance of the piezoelectric element on the charging time.
Still another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that a current for charging the piezoelectric element is measured.
Yet another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that the applied voltage is further adjusted based upon a current for charging the piezoelectric element.
An object of an exemplary embodiment of a method of the present invention is directed to providing a method for operating a fuel injection system having a piezoelectric element for controlling the amount of fuel injected into a combustion engine, characterized in that the piezoelectric element is controlled based upon the charge it is carrying.
Another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that a measured value of a current flowing into the piezoelectric element is obtained and used for determining the charge the piezoelectric element is carrying.
Still another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that a measured value of a current flowing into the piezoelectric element via a current sensor is obtained.
Yet another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that the current sensor comprises a bridge circuit.
Still another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that the current sensor is calibrated.
Yet another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that the measured value of the current flowing into the piezoelectric element via an integrator is integrated.
Still another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that the integrator is calibrated.
Yet another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that the integrator is calibrated using at least one of a first calibration, a second calibration and a third calibration.
Still another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that the first calibration calibrates a reference voltage.
Yet another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that the second calibration calibrates a bridge circuit arrangement.
Still another object of an exemplary embodiment of a method of the present invention is directed to providing the above method, characterized in that the third calibration calibrates a time constant of the integrator.
Yet another object of an exemplary embodiment of a method of the present invention is directed to providing a fuel injection system having a piezoelectric element for controlling the amount of fuel injected into a combustion engine, characterized in that the piezoelectric element is controlled based upon the charge it is carrying.
Further advantages of the exemplary embodiments of the present inventions are also evidenced by the claims, including the dependent claims, and the present description, including the referenced figures.